Dirty carpets are where you really are going to come unstuck. You have to know the limitation of your system and market the market that fits its capabilities.
If you're planning to make a career of this you really need to get the quality aspect of things so they are top notch. This is a results based business and the only way people will come back to you in the future, or as importantly, recommend you to others is if the quality is first class. Encap, although excellent on low profile office carpets is severely limited, especially in the domestic market where you will encounter carpets it simply cannot deal with to the required standard.
Try and have a day out with an experienced professional and get a better view of what you are up against.
Simon